A mathematical approach is given by which the intramyocardial stress sigma induced in the passive medium of the myocardium is expressed as the sum of the stress (sigma)p induced in the passive medium by the left ventricular pressure P and the external pressure Po, and the stress(sigma)d induced in the passive medium by the active force generated by the muscular fibers of the myocardium. Relations between sigma = (sigma)p + (sigma)d, the left ventricular elastance E and the residual volume Vd are also derived. Applications to experimental data are given and clinical implications of the results are discussed.